"Exposures to Air Pollutants and Risk Of Birth Defects" - Birth defects are the leading cause of infant mortality in the US. Our proposed Formative Center's research efforts, will enhance scientific understanding of the potential environmental etiologies of birth defects, which will undoubtedly have important implications for risk assessment and prevention of these common, costly, and often deadly outcomes of pregnancy. In this project (Project 2) we propose to conduct a rigorous population-based epidemiologic study that targets 30 different birth defects. Our research aim specifically proposes to determine whether exposures to specific air pollutants and mixtures of air pollutants, during critical periods of fetal organogenesis, are associated with women delivering infants/fetuses with structural birth defects. In this project we will use data from the largest case-control study conducted to date in the US on birth defects - the National Birth Defects Prevention Study. We will limit our inquiries to the California study site which is being conducted in the San Joaquin Valley - an area with demonstrated poor air quality. To these data, we will provide a much more detailed and specific test of our hypothesis with refined exposure data pertaining to high ambient air pollution. The etiologies of most structural birth defects are unknown. There have been a few observations that point toward ambient air pollutants as risk factors for human birth defects. However, this important public health hypothesis has been under studied owing to the lack of good exposure and outcome data. Thus, Project 2 uniquely fills an important gap in our understanding of the role of environmental exposure on the risk of human birth defects.